1. Field of the Invention
The present invention relates generally to an apparatus and method for diagnosing faults in hot strip finishing rolling, and more particularly to an apparatus and method for diagnosing faults in hot strip finishing rolling, which diagnoses thickness faults in hot strip finishing rolling, using preset data and real-time data on rolling and control conditions, equation models representing control and physical phenomena and a database constructed based on operation experiences.
2. Description of the Related Art
Currently, in the field of hot strip finishing rolling, demands for the improved quality of products are raised and small batch production is used as a manufacturing method, so that a quality control system with higher accuracy is eagerly required.
The manufacturing of hot-rolled products is stably performed under high-accuracy control using a variety of computers and control systems, thus ensuring quality accuracy. However, when a control system is updated or even when the control system is stable, the instability of an operation or the defect of a product occasionally occurs.
The instability of an operation and the defects of products result from a fault in the material of a product, a fault in the operation method of an operator, a fault in rolling facility and a fault in a control system. When the instability of an operation and the defect of a product occur, it must be determined whether a system fault or an operator manipulation fault has occurred, and a counter measure must be taken to prevent the recurrence of the instability of the operation and the defect of the product. To diagnose faults, there have been used a method of comparing and analyzing the actually measured mean data of each product collected and stored in a computer, or performing verification through simulations using the actually measured mean data.
However, since it is necessary to identify causes while viewing an on-line analog data chart when a detailed cause analysis must be carried out, most of cases depend on the manual work of experts. Accordingly, an analysis period is excessively lengthened, and it is difficult to manage the actually measured data.
As a result, to manufacture high quality products using a quality control system, a diagnosis system for supporting the rapid estimation of the causes of a quality fault and a control fault that the operator cannot quickly identify is necessary.
Prior art relating to technologies for diagnosing the quality of a hot strip mill is described below.
First, there was disclosed Korean Unexamined Pat. Publication No. 2001-0027829 filed by POSCO and entitled “Apparatus for diagnosing faults in hot strip mill.”
This prior art patent relates to an apparatus for diagnosing a facility fault and an operation fault in a hot strip mill composed of staged stands. In a steel plant, this fault diagnosing apparatus automatically performs the determination of thickness, shape and facility faults and diagnoses of causes of the faults, so that rapid, accurate diagnoses can be achieved. Diagnosis critical values must be appropriately adjusted so that determination results are matched with diagnosis results. With this adjustment, appropriate critical values can be maintained even when the characteristics of an object are changed, so that high-accuracy diagnoses can always be performed.
However, this prior art patent is constructed to determining whether faults have occurred by simply comparing actually measured values with the critical values. Accordingly, this prior art patent is different from the present invention in that the present invention is a rule-based method. Furthermore, this prior art patent is the technology of automatically changing critical values when the characteristics of an object are changed and performing diagnoses, so that the setting of optimal critical values is an important factor in the success of a diagnosis. However, the setting of optimal critical values is performed according to the type and size of steel, rolling conditions and the situations of a field and, thus, it is considerably difficult to set the optimal critical values.
Second, there was disclosed Japanese Unexamined Pat. Publication No. Hei 11-347614 filed by Mitsubishi Electric Corporation and entitled “Apparatus and method for diagnosing faults.”
In this prior art patent, a deviation between the thickness of a rolled sheet and a target sheet thickness is calculated, and it is determined that a sheet thickness fault has occurred if the calculate deviation exceeds a preset reference value. That is, the local minimal value and local maximal value of a sheet thickness are detected, and it is determined that a thickness fault has occurred if the deviation between the local minimal value and local maximal value exceeds the preset reference value. Additionally, faults are diagnosed based on the balance of a roll speed, the actually measured torque of a mill motor and an actually measured rolling load.
However, since the thickness fault of a hot strip mill is incurred by a variety of causes, this prior art patent cannot perform desirable diagnoses.
Third, there was disclosed Japanese Unexamined Pat. Publication No. Hei 7-251210 filed by Mitsubishi Electric Corporation and entitled “Method of diagnosing faults in on-line roll grinding device.”
This prior art patent is a technology for automatically diagnosing faults in an on-line roll grinding device without depending on operator's unaided eyes. This prior art patent is applied to an on-line roll grinding apparatus that grinds a workpiece while a roll located in a housing is rotated in contact with a whetstone and the whetstone is reciprocated in the direction of a roll axis. In accordance with the prior art patent, the output torque of a whetstone rotating device is detected while the roll is ground by the whetstone, and it is determined that a fault has occurred if the output torque is greater than an upper limit or less than a lower limit.
This prior art patent simply uses threshold values in the same manner as the above-described prior art patents, thus being incapable of fully diagnosing faults.
Fourth, there was disclosed Japanese Unexamined Pat. No. Hei 7-63605 filed by Nippon Steel Corporation and entitled “Apparatus for diagnosing faults in bearing for roll.”
This prior art patent relates to an apparatus for diagnosing faults in a bearing for a roll that is capable of measuring a load applied by the roll to the bearing and diagnosing faults in a wide range. However, this prior art patent has the same disadvantages as the above-described prior art patents.